This research proposes to conduct a national population-based pilot study using explicit criteria to assess both individual and organizational system factors that affect inappropriate use of prescriptions in the elderly. The proposed research has three specific aims: To develop a comprehensive population-based panel database on prescribed medication use for a nationally representative elderly sample derived from the Medical Expenditure Panel Survey (MEPS). The database will be a result of matching and augmenting the MEPS medication sample with additional descriptive drug information from the National Drug Code Directory database. To document the most recent national patterns and time trend of inappropriate prescriptions in the elderly, for both general and disease- specific cohorts. The inappropriateness of prescriptions for the elderly will be assessed by the most recently updated explicit criteria developed by Bears (1997). To analyze how individual and organizational characteristics affect the probability as well as the quantity of inappropriate prescriptions by the elderly in the context of a two-part model framework controlling for patient characteristics and disease conditions. Organizational structures will include pharmacy sources of care for medical and pharmacy services, insurance type, and medical care organizational features. This study design is warranted on three major grounds. First, inappropriate predescribing contributes to substantial adverse drug events (ADEs), which account for a majority of medical adverse events. Second, elderly are at much higher risk for ADEs than younger people. Third, existing research has not satisfactorily distinguished how individual and organizational features contribute differently to the likelihood vs. The quantity of inappropriate predescribing in the elderly.